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How do monocytes become macrophages after entering body tissues?

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Illustration of a blood vessel with a cutaway view showing red blood cells, white blood cells, platelets, and plasma, each labeled to highlight the main components of blood. — white blood cell Blood is made up of multiple components, including red blood cells, white blood cells, platelets, and water-rich plasma.

After entering body tissues from the bloodstream, monocytes undergo a process of differentiation to become macrophages. This transformation is primarily guided by local environmental signals, specifically cytokines and growth factors.1

The presence of colony-stimulating factors, most notably macrophage colony-stimulating factor (M-CSF), triggers the development of monocytes into macrophages. Once differentiated, these cells serve essential roles in the immune system by engulfing and destroying pathogens, clearing cellular debris, and regulating inflammation. Depending on the specific cues they receive within the tissue environment, these macrophages can further polarize into different phenotypes, such as pro-inflammatory (M1) or anti-inflammatory (M2) states.1